A helicopter is commonly fitted with one or more hundreds of electrical harnesses, and they can all be different from one another.
An electrical harness is usually made up of lengths of sheathed (insulated) electrically conductive wire collected together and/or tied together so as to form distinct portions, or branches, of the harness; the harness also generally comprises one (or more) electrical connectors disposed at a free end of at least one of the branches; each connector is mechanically secured to the end of at least one of the wire segments forming the branch in question; a connector includes at least one male or female electrical connection member (or terminal) which is in electrical contact with the end of one of the segments of wire, e.g. by being crimped thereto, and possibly after said end has been stripped.
Manufacturing a harness essentially consists in bringing together and/or uniting wire segment portions so as to build up the branches of the harness, and in fitting suitable connectors to the ends of the branches of the harness, where appropriate.
The manufacture of an electrical harness for a helicopter generally also includes an operation of providing the branches with electromagnetic or mechanical protection by means of a braided sheath.
Such protection makes the harness stiff, and thus makes it difficult to put the harness into place. To mitigate this drawback and to leave a degree of flexibility to the harness, it is necessary to twist the cables making it up prior to braiding on the sheath.
As a general rule, in order to manufacture a harness, use is made of a plane support, such as a bench or table, to support the electrical harness; the table may be fitted with a jig on which there appears a representation of the path to be followed by the wires or cables of the harness, as described in particular in patent application FR 2 808 374 and WO 01/82313; an operator places segments of wire on the jig in compliance with the representation, and then makes the electrical connections to the ends of the branches of the harness.
A drawback of that technique is that it requires the use of a table and a jig of shape and dimensions that match those of the harness when complete and deployed (“spread out”).
In order to provide assistance in putting the wire segments into place and in keeping them on the support or jig, it is possible to fit the jig with guide pegs that serve to form bends or bifurcations in the deployed harness; it is also possible to use clamps for holding each end of a wire segment, as described in particular in U.S. Pat. No. 5,205,329.
Such devices for manufacturing electrical harnesses are complex and bulky; they are unsuitable for manufacturing helicopter electrical harnesses which can have ten or more branches, and which can extend over a length of ten or more meters.
Such devices also do not make it easy to twist the wires of the harness; when such twisting is performed manually, the wires do not wind into a regular helix; in particular, when the branch and/or the harness to be twisted has a first wire of large section and a second wire of smaller section, the first wire tends to oppose twisting, and as a result, manual twisting of such a branch or of such a harness generally leads to the second wire winding around the first wire which does not itself become helically shaped; because of this lack of twisting, harmful stress can arise in one or more wire segments when the harness is bent or curved.